The present invention relates generally to computer peripheral storage apparatus, and more particularly, to an improved linear actuator for reciprocably positioning an objective lens actuator assembly relative to a rotating optical disk on which information is recorded.
Both magnetic and optical disk storage devices have been used as peripheral equipment for computers. In these devices, the disk is typically rotated at a uniform speed and a magnetic head or laser-focusing objective assembly is reciprocated by a linear actuator in a radial direction in order to select a particular data track.
Most linear actuators used for accessing tracks of a memory disk are of the moving coil, fixed magnetic circuit type. Referring to FIG. 1 herein, a typical linear actuator comprises a magnetic circuit 10, a wheeled carriage 12, a coil 14 mounted to the carriage and slideable linearly over the pole or stator of the magnetic circuit, and guide rods such as 16 over which the wheeled carriage rides. A payload 18 is supported by the carriage for reciprocal linear movement in a radial direction relative to a rotating disk 20 supported by a spindle 22. Where the disk is the magnetic type, the payload comprises a read/write head which is positioned very close to the surface of the rotating disk. Where the disk is the optical type, the payload comprises an objective lens actuator assembly for focusing a laser beam on a particular spot on the disk in order to read the same.
In a typical linear actuator, it is desirable to minimize the clearance between the magnetic pole and the moving coil bobbin in order to optimize the magnetic flux in the air gap and thereby maximize the driving force and minimize access time. In order to guarantee accuracy of the coil bobbin-to-pole relationship, it is necessary to precisely control the location and angularity of the carriage and rods relative to the magnetic circuit to ensure even distribution of clearances nominally over the entire stroke of the linear actuator. The mechanical parts of a typical linear actuator must therefore be manufactured to very close tolerances at considerable cost.
Another drawback of conventional linear actuators is that they take up an undesirably large amount of the space available in the physical envelope allowed for the disk drive. This is especially true where the disk drive is constructed to meet the computer industry standard five and one-quarter inch form factor, i.e. a rectangular volume measuring three and one-quarter inches in height by five and three-quarter inches in width by eight inches in length. In an optical disk drive, it is desirable to reserve the space behind the carriage, normally occupied by the magnetic circuit for the fixed optics. Furthermore, in an optical disk drive where the optics are divided into fixed and movable portions, alignment of the optical axis to the axis of travel of the carriage becomes critical.
U.S. Pat. Nos. 4,414,594; 4,504,935; and 4,554,653 disclose relevant linear actuators.